With recent rapid progress in the field of the electric and electronic industries, electric and electronic devices have been made higher in performance, smaller in size and portable. With such developments of these devices, there has been an increased requirement for secondary batteries which are capable of recharging and have a high energy density so as to be adaptable for use in these electronic devices.
As for the conventional secondary batteries used for these electronic devices, lead acid batteries, nickel-cadmium batteries and nickel-hydrogen batteries are enumerated. However, a battery which has a higher energy density than these has been required. Recently, lithium secondary batteries comprising the combination of (1) a negative electrode using a metallic lithium, a lithium alloy, a carbon material or the like capable of electro-chemically occluding and releasing lithium ions as an active material for the negative electrode and (2) a positive electrode using a lithium-contained complex oxide, a chalcogen compound or the like as an active material for the positive electrode have been researched, developed and partly put to practical use. This type of battery is high in battery voltage and larger in energy density per weight and volume as compared with the above-mentioned other types of conventional batteries, and is a most promising secondary battery for the future.
Either a positive electrode plate or a negative electrode plate to be used for this kind of battery is produced by a method wherein a binder, an electric conductive agent, etc. are added to and mixed with an active material thereof, and an active material mixture agent thus obtained is mixed in a dispersing agent to prepare a coating slurry of the active material mixture agent, and the coating slurry thus obtained is coated on a collector, dried and pressed. Improving the characteristics of the battery depends not only on the selection of such materials as active materials, to start with, binders added therein and dispersing agents etc., but also on how to produce a good electrode by using the selected materials. Above all, if the adhesion between the active material mixture agent and the electric collector is insufficient, degradation of a cycle characteristics of a battery or the like result, even if good materials are selected. Accordingly, to improve the adhesion, examination of most suitable selection of kinds of the binders and the optimum addition amount of the binders, examination of the drying conditions for removing the dispersing agents and other various examinations have been carried out. (See publications of JP-A 4249860, JP-A 5290836, JP-A 5290837 and JP-A 5182692)
However, the positive electrode and the negative electrode produced by the above mentioned conventional techniques involve such inconveniences that the battery characteristics of the lithium secondary batteries, especially the charge-discharge cycle characteristics cannot be sufficiently obtained, and a quick decrease of the battery capacity results. One of the causes thereof is considered to be the insufficient adhesion between the active material mixture agent and the collector.
Accordingly, in view of the above-mentioned inconveniences, the development of a method of producing an electrode which improves of the adhesion between the active material mixture agent and the collector and also improves of the charge-discharge cycle characteristics of a lithium secondary battery is desired.